Vector3 Expected; got nil?

Working on a GUI when I stumbled on an error with vector3's. An error on line 8

local function GenerateSelectionModel()
    if SelectionModel then
        SelectionModel:Destroy()
    end
    local Prefab = PrefabTable[SelectionNumber]
    if Prefab then
        SelectionModel = Prefab:Clone()
        SelectionModel:SetPrimaryPartCFrame(CFrame.new(Mouse.Hit.p) * CFrame.Angles(0, math.rad(CurrentRotation), 0) * CFrame.new(SelectionModel:FindFirstChild("Compensation")) or {Value = Vector3.new() * CFrame.new(0, SelectionModel.PrimaryPart.Size.Y / 2, 0)})
        local Cache = SelectionModel:GetDescendants()
        Mouse.TargetFilter = SelectionModel
        for i = 1, #Cache do
            if Cache[i]:IsA("BasePart") then
                Cache[i].Material = Enum.Material.Glass
                if Cache[i]:IsA("UnionOperation") then
                    Cache[i].UsePartColor = true
                end
                if Cache[i]:IsA("Seat") then
                    Cache[i].Disabled = true
                end
                if Cache[i].Transparency ~= 1 then
                    Cache[i].Transparency = 0.5
                end
                Cache[i].CanCollide = false
            end
        end
        if Equipped then
            SelectionModel.Parent = PrefabsFolder
        end
    end
end

This is a local script inside StarterCharacterScripts; if you need more information do ask. Thanks